Effect of Dynamic Ageing on the Stability of Oil-in-Water Emulsions with Anionic and Nonionic Surfactants in High-Salinity Water

Oily wastewater in the bilge of ocean vessels (i.e., bilge water) makes oil removal difficult due to the generation of oil-in-water (O/W) emulsions. A ship's motion can promote emulsification or coalescence, depending on the surfactant type and concentration. This study investigates the effects of motion on model bilge water O/W emulsions, which has yet to be published in the literature. Mineral oil, 0.42 M NaCl DI-water, and a nonionic surfactant (Triton X-100) or an anionic surfactant (sodium lauryl ether sulfate, SLES) served as a model bilge water emulsion. The stability was characterized under static and dynamic conditions via optical microscopy and light diffraction. Ship motion was mimicked using a three-dimensional rocker. Under static conditions, the surfactant-to-oil ratio (S/ O) needed to stabilize the emulsions for up to 20 days was 0.2 for SLES and 0.1 for Triton X-100. During dynamic ageing at 12 rpm, the S/O to promote emulsification was 0.1 for SLES and 0.2 for Triton X-100. At 30 rpm, the S/O to promote emulsification was 0.02 for SLES and 0.1 for Triton X-100, suggesting a complex interplay between surfactant concentration and energy input. These results expand on existing knowledge of bilge water and potentially reducing ocean pollution.